(1) Field of the Invention
The present invention relates to a method and to a device for detecting icing at an air inlet of a turboshaft engine. The invention is situated more particularly in the field of systems for detecting icing of an engine of an aircraft.
(2) Description of Related Art
An aircraft, and in particular a rotorcraft, can encounter icing conditions while in flight. Thus, ice can accumulate on certain portions of the aircraft as a function of atmospheric conditions.
More precisely, ice can become deposited on members of an air inlet. For example, the engine may have a grid protecting the air inlet that is in danger of picking up ice in icing environmental conditions.
The ice can tend to obstruct the air inlet, at least in part.
The ice can also become detached and can be ingested by the engine. Ingested ice can then damage the blades of the engine compressor and/or can give rise to flame-out of the engine.
Under such circumstances, certain aircraft are not authorized to fly in icing conditions. In spite of this prohibition, certification regulations require a manufacturer to demonstrate that flight in icing conditions is possible during some limited length of time.
This limited length of time is determined as a function of the time needed for a pilot to become aware of the presence of icing conditions and/or of the time needed to exit icing conditions, e.g. by coming closer to the ground.
Other aircraft are provided with devices for flying in limited icing conditions. Such devices can than be activated during a stage of flight in icing conditions.
Independently of the ability of the aircraft to fly in icing conditions, a system of the aircraft or a crew member may be required to determine that icing conditions are present.
Such detection of icing conditions sometimes relies on the ability of the pilot to detect such conditions. A measurement of the outside temperature is not sufficient to be able to assert that an aircraft is flying in icing conditions. Under such circumstances, a pilot can sometimes detect the presence of icing conditions by observing the windshield of the aircraft or certain pieces of equipment having an opening to the outside. Thus, the presence of ice on the windshield or on external probes is the main indicator of icing conditions for a pilot.
Certain aircraft may then for example be fitted with ice sensors. The location of ice sensors needs to be selected with care.
Document U.S. Pat. No. 6,304,194 B1 describes a method of detecting icing on a tilting rotor of an aircraft. The rotor is capable of tilting from a hovering flight position to a forward flight position, so arranging ice sensors can be difficult.
In that method, the torque of the rotor is measured, which torque is referred to for convenience as the “measured” torque, and the thrust generated by the rotor is also measured, which thrust is referred to as the “measured” thrust, by convenience. The measured torque and the measured thrust are then compared with a model and an error signal is generated as a result of the comparison.
In addition, the signal transmitted by an icing sensor is transmitted to the model, and said error signal is modified as a function of that comparison.
Document WO 2008/138846 describes a method based on using a test device.
Thus, a surface of the test device is covered in a material liable to pick up ice. The surface is then caused to move at a predetermined speed for a predetermined length of time.
The thickness or the weight of ice picked up is then measured in order to determine the concentration of supercooled snow and water in the air.
Document EP 2 657 133 presents a device for providing protection against icing, which protection is provided in particular by using an icing sensor to control energy sources for combating the formation or the accumulation of ice.
Document EP 2 110 314 is remote from the problem of detecting icing conditions, since it proposes a method and a device for providing protection against icing. Such a device includes electric heater components.
Likewise, Document U.S. Pat. No. 8,049,147 describes a system having three heaters for preventing icing of a turbine.
Document U.S. Pat. No. 7,374,404 is also remote from the problem of the invention. Specifically, Document U.S. Pat. No. 7,374,404 suggests applying a polyurethane coating on certain portions of a blade of a gas turbine engine in order to prevent excessive accumulation of ice.
Document US 2014/0090456 is remote from the invention.
According to Document US 2014/0090456, the temperature and the pressure of air at the inlet to a gas turbine engine compressor needs to be monitored specifically for properly controlling the engine. The temperature and pressure may be used for detecting the presence of icing.
Under such circumstances, Document US 2014/0090456 describes a system for detecting a measurement fault on the basis of a theoretical model of the engine, of a comparator module, and of an estimator module for estimating inlet conditions.
The engine model serves to establish the estimated value of at least one engine parameter, each engine parameter being selected from a list including the speed of rotation of a rotary member of the engine, a combustion pressure, and an exhaust gas temperature.
The comparator module is then configured to establish the difference between the measured values of those engine parameters and the estimated values.
The difference is used by the estimator module in order to adjust the engine inlet parameters used by the engine control relationship. Those inlet parameters include the temperature and the pressure of the air at the inlet to a compressor of the engine.
Furthermore, sensors measure the value of those inlet parameters.
If the measured values of the inlet parameters differ from the estimate made by the estimator module, then an error signal is issued. Furthermore, the estimated inlet parameters are used for generating the control relationship. Otherwise, the measured inlet parameter values are used for generating the control relationship.
Documents GB 2 259 895 and GB 2 046 690 are also known.
Document EP 2 623 746 is remote from the invention, which seeks to detect icing conditions, since that Document EP 2 623 746 seeks to optimize performance.